How can I capture SQL execution plan for queries . Someone told that I can retrieve them through system tables
As gbn points out, there are a number of different ways that you can review the execution plans for queries. Given that your question makes reference to the use of system tables I assume that your are talking about the Dynamic Management Views (DMV's) and that your are therefore also only interested in query plans that are currently in the plan cache.
If you are interested in identifying the query plan for a specific query from the plan cache then you can use a query of the form like below:
SELECT deqs.plan_handle ,
deqs.sql_handle ,
execText.text
FROM sys.dm_exec_query_stats deqs
CROSS APPLY sys.dm_exec_sql_text(deqs.plan_handle) AS execText
WHERE execText.text LIKE '%QueryText%'
For further reading, take a look at the article DMVs for Query Plan Metadata
If say you are more interested in reviewing the performance of your most poorly performing queries, that are currently referenced in the plan cache, you can make use of the excellent and freely available
SQL Server Performance Dashboard Reports.
There are of course other methods for viewing query plans but without knowing exactly what it is that you are trying to achieve, these may not be appropriate to your needs.
Quick search on MSDN will get you this: http://msdn.microsoft.com/en-us/library/ms189747.aspx
Hope it helps.
This question could be clearer but I imagine some people coming here might be looking for the easiest way to get an execution plan for a query
The easiest way to capture the execution plan of a query is to click the "Include Actual Execution Plan" button and execute the query on SSMS
Results will be displayed as a tab together with the query results
Related
A synchronization program is syncing data between our SQL server and an online database. Every 5 minutes the program runs query's on all tables, al in the format:
select max(ID) from table
After that, the program retreives information from the online database, using the max(ID) to retreive only newer records.
The query runs fast on small tables, but some tables have millions of records.
The performance can be boosted by using a Where statement:
select max(ID) from table where date >= dateadd(dd,-30,getdate())
Unfortunately it's an old program, which cannot be changed anymore.
(no supplier and no source code)
I read something about Plan Guides, which should give performance boosts to query's.
Can I use a plan guide to alter these query's so they run much faster??
I would try to stay clear of plan guides unless you have tried everything else to help SQL Server choose a better execution plan; reason, you are forcing SQL Server to choose maybe not the best execution plan and if your statistics are right, SQL Server does a heck of a job to provide you with a very good estimation plan.
Sorry if this is going to be long winded but SQL Server performance is based on statistics and if your statistics are off, your query will not perform optimally. This is where I would first start.
I would first run your query and generate an estimated execution plan and actual execution plan. If you have never worked with execution plans, here are a few sites to start you off to understand operators and how to interpret some of the more common operators; Rasanu Consulting (Joins), Microsoft (Joins), Simple Talk (Common Operatiors), Microsoft (All Operators). The execution plans are generated from statistics SQL Server stores on indexes and non-indexed columns. I am assuming your query is stored in a procedure where the initial execution plan is stored. Unfortunately, changes to the query in the stored proc can cause performance issues because of an outdated plan and the proc will need to be recompiled.
Based on the results of your execution plan, you may find a simple clustered index will help performance or find that fine tuning your where clause will result in better carnality estimates. Here are a few sites that do a really good job explaining statistics; Patrick Keisler, Itzik Ben-Gan, Microsoft
You may be wondering "what does this have to do with my question?" which would expect a simple yes or no answer but, effectively correcting query performance starts with an understanding statistics and execution plans.
Hope this helps!
Here is the question:
I am using VisualCron to run a ssis package on SQL Server 2008 R2. The SSIS package will run a query which get millions of rows and output it into a flat file. Sometimes, I found when I run this SSIS package, the sql server doesn't use multi-threading(I can tell that from the activity monitor) , this lead to very long running time about 20 hours. But, if it was using multi-threading it could be done in 8 minutes.
Is there a way to force sql server to use multi-threading whenever it is running this SSIS package?
There are a few options for optimizing your query to handle multiple simultaneous operations... or at least improving performance.
Apply OPTION MAXDOP in your query to apply the maximum number of processors (parallelism) available with the operating system. Listed below is an example and here is a link with more detail.
SELECT FirstName, LastName
FROM dbo.Customer
OPTION (MAXDOP 1)
Apply NOLOCK in the your query if there is no concern with data in the tables being updated during the SSIS package operation. That is, this works if there is no concern with "dirty reads." See following link and example.
SELECT FirstName, LastName
FROM dbo.Customer WITH(NOLOCK)
Review this link for best practices for improving query performance. There may be additional steps you have not taken or tools you have not applied that can greatly assist in improving performance.
The problem is getting clearer.
It's related to how sql decide to use a serial execution plan or a parallel execution plan. That's the optimizer's job. It turns out that I have two tasks in VisualCron that are scheduled to run, they both will run the same big query. The difference is they will get different input parameters.
The first one get parameters that will not deal with too much data.
The second one get parameters that deal with a big amount of data.
I assume the SQL optimizer first see the submitted query, and the query will not get too much data, so it decide to use serial plan.
I guess the plan for this same query is cached, so when it check the second submitted query, the optimizer might check the cache to see if any past evaluated plan exist for this query. Then, if it exist, it will use it.
That's why it still choose to use serial plan for the second query.
After I change the order of the two task(I execute the one which will deal with more data first, and then the one that deal with less data), it works, it is now using parallel plan for both. (You may need to restart the instance to clear the cached execution plans)
How the optimizer works is still my assumption.
Other people's post, explaining how optimizer are playing a important role here
http://web.archive.org/web/20180404164406/http://sqlblog.com/blogs/paul_white/archive/2011/12/23/forcing-a-parallel-query-execution-plan.aspx
I have a bunch of Informix queries and I need to verify the performance of each query.
All these queries are long and contain a lot inner SELECT and JOINs. So I am wondering if there is any tool which can assist me to check which fragment in the query affects the whole query performance?
It would help a lot because it's hard to check only by eyes.
If you want to analyze queries then use Informix SET EXPLAIN and analyze output file it creates. Have a look at IBM documentation: http://www.ibm.com/developerworks/data/library/techarticle/dm-0409fan/index.html?S_TACT=105AGX52&S_CMP=cn-a-db2
What is the usage of Execution Plan in SQL Server? When can these plans help me?
When your queries all run fast, all is good in the world and execution plans don't really matter that much. However, when something is running slow, they are very important. They are primarily used to help tune (speed up) slow SQL. Without execution plans, you'd just be guessing at what to change to make your SQL go faster.
Here is the simplest way they can help you. Take a slow query and do the following in a SQL Server Management Studio query window:
1) run the command:
SET SHOWPLAN_ALL ON
2) run your slow query
3) your query will not run, but the execution plan will be returned.
4) look through the PhysicalOp column output for the word SCAN within any text in this column, this is usually the part of the query that is causing the slowdown. Analyze your joins and index usage in regards to this row of the output and if you can eliminate the scan, you will usually improve the query speed.
There are may useful columns (TotalSubTreeCost, etc) in the output, you will become familiar with them as you learn how to read execution plans and tune your slow queries.
When you need to perform performance profiling on a specific query.
Have a look at SQL Server Query Execution Plan Analysis
When it comes time to analyze the
performance of a specific query, one
of the best methods is to view the
query execution plan. A query
execution plan outlines how the SQL
Server query optimizer actually ran
(or will run) a specific query. This
information if very valuable when it
comes time to find out why a specific
query is running slow.
It's helpful in identifying where bottlenecks are occurring in long running queries. You can make some quite impressive performance improvements simply by knowing how the server executes your complex query.
If I remember correctly it also identifies good candidates for indexing which is another way to increase performance.
These plans describe how SQL Server goes about executing your query. It's the result of a cost-based algorithm by the SQL Server query optimiser, which comes up with a plan for how to get to the end result in the expected best possible way.
It's useful because it will show you where time is being spent in the query, whether indexes are being used or not, what type of process is being done on those indexes (scan, seek) etc.
So if you have a poorly performing query, the execution plan will highlight what the costliest parts are and allow you to see what needs optimising (e.g. may be a missing index, may be an inefficiently written query resulting in an index scan instead of a seek).
sys.dm_exec_query_stats seems to be a very useful function to gather statistics from your database which you can use as a starting point to find queries which need to be optimized. selecting * gives somewhat cryptic results, how do you make the results readable? What type of queries do you get from it? Are there other functions or queries you use to gain performance statistics?
To make the results useful, you need to cross reference the information with a few other DMV's and also concentrate your analysis and tunning efforts on the most poorly performing queries.
Here is (one I made earlier) an example of using the DMV you have mentioned to identify the most costly SQL Server queries.
How to identify the most costly SQL Server queries using DMV’s
You can easily extend this to look at other metrics too.
If you want to make performance tuning a breeze for yourself, you should consider installing the freely available SQL Server Performance Dashboard Reports.
These can be used to identify SQL Server Waits, the queries that consume the most I/O, the longest running queries by duration etc.
Why don't you first use 'set pagesize 0'.